Stereomicroscopes constructed as operating microscopes are described in detail for example in W. H. Lang, F. Muchel. “Zeiss Microscopes for Microsurgery”, published by Springer, Berlin, Heidelberg, New York, 1981. Ophthalmological microscopes are also described therein. These have a main objective, a magnification system provided downstream thereof and a binocular tube with eyepieces. In order to produce a stereomicroscope, in a magnification system constructed as a zoom system, for example, the optical path passing through the main objective may be split into a number of optical paths in order for example to enable the object to be viewed simultaneously by a first user (main operator or surgeon) and a second user (assistant).
For intraocular surgery, for example to make it possible to observe the fundus or parts of the vitreous humour close to the fundus of a human eye, additional optical means are required on the stereomicroscopes. These consist of lenses that are provided upstream of the main objective (on the object side).
Additional optical means of this kind are known from the brochure “SDI II, Biom II” by Okulus Optikgeräte GmbH, dating from 1998, and from U.S. Pat. No. 4,856,872. They comprise a lens that is to be arranged close to the object to be observed (ophthalmoscopic lens) and a lens arranged closer to the main objective (reduction lens).
From DE 41 146 46 C2, a solution is known in which an ophthalmological attachment is housed in an attachment housing that can be positioned to the side of the main objective. The attachment comprises an ophthalmoscopic lens, an optical system for image rectification and a movable lens (correcting lens) for focusing.
A system for image rectification is needed as the additional optical means display the microscopic image vertically and laterally reversed (inverted) and hence pseudostereoscopically to the viewer. This means, among other things, that the intermediate image generated by the ophthalmoscopic lens shows the foreground and background reversed in depth perception. However, to be able to perform microsurgery, a rectified image is essential.
Special additional optical means used in eye surgery are so-called wide-angle observation systems which make it possible to look into the interior of the eye, providing a large viewing angle. For this, the ophthalmoscopic lens has to be arranged as close as possible to the eye. Viewing angles of up to about 130° can be achieved, while a distinction is made between contact and non-contact systems depending on whether or not the eye is touched. One unwanted side-effect even with such large observation angles is the fact that the images generated are also diagonally inverted.
Typically, these effects are corrected using a special system of prisms (inverter system). In connection with this, reference may be made by way of example to the EIBOS system of the company Müller-Wedel, which is advantageous in that the inverter is already provided underneath the microscope and delivers the correct image to the microscope. However, this system is regarded as optically relative complicated. In addition it is relative bulky and heavy.